BEIJING (AFP) - China's pollution reached new heights on Friday, as the Tibetan capital of Lhasa was shrouded in a cloud of dust that halted flights and rendered one of its most-recognisable landmarks nearly invisible.

Lhasa, which at 3,700 metres above sea level is one of the highest cities on the world, was named by China's Ministry of Environmental Protection last month as one of 10 cities with the country's best air quality.

But on Friday, the picturesque capital of the Tibetan region was enveloped in a thick cloud of pollution that the Hong Kong-based ifeng.com news website said was caused by dust that had blown in from north of the Tibetan Plateau.

Visibility in some areas was reduced to five kilometres, flights were grounded, and the city's air quality index exceeded 500, the highest level, the report said.

Photos posted online by ifeng.com showed the world-famous Potala Palace, a sprawling Buddhist complex and Unesco World Heritage site that previously served as the winter palace of the Dalai Lama, nearly invisible from a few kilometres away.

The images of pollution in the remote tourist destination, as opposed to in the industrial cities of northeast China, took users of the country's popular social networks by surprise.

"Even Lhasa has floating dust," wrote one. "Heaven on Earth is gone."

"It proves again that Lhasa is the sacred inseparable territory of China," quipped another, in a nod to the tensions between Beijing and Tibetans seeking greater autonomy for the region.